Spatially Resolved Operando Synchrotron Studies of Li Metal Anode Stripping and Plating - Heterogeneity and Correlations with Cathode Performance

<i>Operando </i>high energy lateral mapping (HELM) synchrotron diffraction studies have been used to carry out spatially resolved studies of the stripping and plating of Li metal anodes during battery cycling. Although it is very challenging to directly quantify the signal from Li metal layers that are only a few microns thick, this can be accomplished when the data collection is carried out in a carefully designed experiment at a modern synchrotron source and the subsequent Rietveld refinements are performed with suitably constrained structural models. In this manner, we have been able to interrogate the heterogeneity that develops during the cycling of “anode-free” pouch cell batteries with different metals used as the current collector. Furthermore, our data has enabled us to identify correlations between the heterogeneity in the anode and the cathode as well as to better understand the effect of this heterogeneity on the local current densities at different regions of the anode. Our synchrotron measurements probe local variations in electrochemical performance that cannot be resolved through traditional electrochemical testing, thereby providing novel insights into processes contributing to the loss of capacity and the reduction in the lifetime of pouch cell batteries.